Chapter III, Part 1. Offices and Ministries in the Celebration
22. The principles of active and conscious participation are in a sense even more significant for Masses celebrated with children. Every effort should therefore be made to increase this participation and to make it more intense. For this reason as many children as possible should have special parts in the celebration: for example,; preparing the place and the altar (see no. 29), acting as cantor (see no. 24), singing in a choir, playing musical instruments (see no. 32), proclaiming the readings (see nos. 24 and 47), responding during the homily (see no. 48), reciting the intentions of the general intercessions, bringing the gifts to the altar, and performing similar activities in accord with the usage of various peoples (see no. 34).
To encourage participation, it will sometimes be helpful to have several additions, for example, the insertion of motives for giving thanks before the priest begins the dialogue of the preface.
In all this, it should be kept in mind that external activities will be fruitless and even harmful if they do not serve the internal participation of the children. Thus religious silence has its importance even in Masses with children (see no. 37). The children should not be allowed to forget that all the forms of participation reach their high point in eucharistic communion, when the body and blood of Christ are received as spiritual nourishment. 
23. It is the responsibility of the priest who celebrates with children to make the celebration festive, familial, and meditative.  Even more than in Masses with adults, the priest is the one to create this kind of attitude, which depends on his personal preparation and his manner of acting and speaking with others.
The priest should be concerned above all about the dignity, clarity, and simplicity of his actions and gestures. In speaking to the children he should express himself so that he will be easily understood, while avoiding any childish style of speech.
The free use of introductory comments  will lead children to a genuine liturgical participation, but these should be more than mere explanatory remarks.
It will help him to reach the hearts of the children if the priest sometimes expresses the invitation in his own words, for example, at the penitential rite, the prayer over the gifts, the Lord's Prayer, the sign of peace, and communion.
24. Since the eucharist is always the action of the entire ecclesial community, the participation of at least some adults is desirable. These should be present not as monitors but as participants, praying with the children and helping them to the extent necessary.
With the consent of the pastor or rector of the church, one of the adults may speak to the children after the gospel, especially if the priest finds it difficult to adapt himself to the mentality of children. In this matter the norms soon to be issued by the Congregation for the Clergy should be observed.
Even in Masses with children attention is to be paid to the diversity of ministries so that the Mass may stand out clearly as the celebration of the community.  For example, readers and cantors, whether children or adults, should be employed. In this way a variety of voices will keep the children from becoming bored.